Recently, ceramics of calcium phosphate series compounds such as apatite hydroxide [Ca.sub.10 (PO.sub.4).sub.6 (OH).sub.2 ], tricalcium phosphate [Ca.sub.3 (PO.sub.4).sub.2 ] and the like are expected as an implant material for artificial tooth root, artificial bone or the like because of excellent bioaffinity. However, these calcium phosphate compound ceramics cannot be said to have sufficient strength and toughness against mechanical impact or stress produced when being used as the artificial bone or tooth root, so that they are not yet put into practical use at present.
Under obtaining the above circumstances, there have hitherto been made many studies and developments for obtaining implant materials having excellent affinity to biotexture as well as excellent strength and toughness. Among them, composite ceramics obtained by adding heat-resistant inorganic short fibers to the calcium phosphate series compound ceramic are highlighted as effective ones.
For instance, there are proposed "Artificial tooth, artificial bone and method of producing the same" in Japanese Patent Application Publication No. 59-219, "Carbon fiber-apatite series composite fired bodies" in Japanese Patent Application Publication No. 61-41876, "Mineral fiber-apatite series composite fired bodies" in Japanese Patent laid open No. 59-57971 and the like as a related technique, and also there is a study by Iida, Iijima et al., "Fiber reinforced apatite through pressurized sintering so as to orient mild carbon fibers into long axis direction" in Association of Japan Ceramics, abstract collection for forum, forum item number 3G09.
In the case of the above conventional techniques, the toughness of apatite is somewhat improved, but there are not yet developed high density fiber reinforced apatites satisfying conditions required as an implant material for artificial bone, artificial tooth root or the like, i.e. having excellent strength and toughness.
That is, the high density fiber reinforced apatites produced by these known techniques have a drawback that a large shrinkage is caused during the sintering because a relatively low density green shaped body is forcedly densified by sintering under a pressure. In other words, the heat-resistant inorganic fibers such as whisker and the like contained in the green shaped body are subjected to a large deformation during the pressurized sintering or broken in extreme cases. Furthermore, the mixture of powder and fibers is merely fired, so that the adhesion property between the fiber and the powder matrix is poor. Therefore, the toughness and also the strength are not so improved though the heat-resistant inorganic fibers are added.
Furthermore, in the above conventional techniques, the heat-resistant inorganic fibers are apt to be oriented in a two-dimensional direction, so that the anisotropy is caused in the strength and toughness, and consequently there should be considered the anistropy in use.
It is an object of the invention to propose fiber reinforced ceramics of calcium phosphate series compounds capable of advantageously solving the above drawbacks of the conventional technique as well as a method of producing the same.